The present invention relates to a silicone rubber composition having a high stability in the presence of steam and/or long-life coolant (LLC), such as anti-freeze solution, which comprises water, polyethylene glycol, and a rust-preventive composition.
Conventionally, in order to produce a silicone rubber composition having excellent physical properties, a mixture consisting of a so-called raw rubber, which comprises a silicone polymer and a silica filler, is used as the base compound. The silica filler may be a hydrophilic fumed silica or a hydrophobic fumed silica. Of these, the hydrophobic fumed silica is capable of mixing well with the raw rubber, and the resulting composition will have little tendency toward crepe hardening and will have excellent strength and transparency. Further, where a hydrophobic fumed silica is used in a process for producing a rubber composition, the temperature and time required to mix the filler with raw rubber are more economical than when other kinds of silica filler are employed. Among such hydrophobic fumed silicas which are in the public domain are ones which have specific surface areas of 50 m.sup.2 /g or greater and which bear the groups Me.sub.3 SiO1/2 and Me.sub.2 SiO on their surfaces (Me stands for methyl).
The treatment of the surface of a silica with a silazane compound, such as organocyclosiloxane and hexamethylene disilazane, is known in the art (U.S. Pat. Nos. 2,938,009; 3,004,859; 3,024,126; and 3,635,743). U.S. Pat. No. 4,985,477 teaches treating the surface of a filler with a mixture of MeSiO.sub.3/2 and Me.sub.2 SiO. U.S. application Ser. No. 07/467,431 relates to a composition containing a surface-treated filler. The prior art does not teach the use of dimethylchlorosilane as a surface treater to attach the hydrophobic MeSiO.sub.3/2 and Me.sub.2 SiO groups to the surface of the silica.
However, the demand for quality silicone rubbers used as industrial materials, such as construction materials and parts of electric and electronic appliances, automobiles, business machines, and household utensils, e.g., food containers, rice boilers, thermo pots, etc., has become so keen that the only silicone rubbers suitable are those that have diverse, as well as excellent, properties, whereby they can perform their functions stably under stricter conditions than were formerly expected. However, conventional silicone rubbers do not have sufficient durability against steam and LLC (e.g., anti-freeze solution) to dependably maintain their functions in their presence.